1. Field of the Invention
The present invention relates to a semiconductor wafer impurity diffusion apparatus, and more particularly to an open tube-type impurity diffusion apparatus apparatus for simultaneously diffusing an impurity over a plurality of semiconductor wafers which are all being exposed in common to the same set of environmental conditions.
2. Description of the Prior Art
In general, an open tube-type impurity diffusion apparatus for diffusing impurities over a semiconductor wafer includes a diffusion box which is mainly made of graphite and is shown in FIGS. 2A, 2B and 2C. In FIGS. 2A, 2B and 2C, a wafer 3 is shown horizontally placed in a slider 4 located on a plate 6, which is covered with wafer cover. The wafer is covered with the wafer cover at the stage depicted in FIG. 2, in order to prevent degradation of a surface of the wafer due to an atomic secession from the surface of the wafer under a diffusion process of high temperature.
A diffusion source for diffusing the wafer is taken in a diffusion box 1 located on the slider 4. Then, the slider sets a temperature of the furnace, in which a heater 5 is built, to a required diffusion temperature.
After the required temperature setting, the slider 4 is pushed to the arrow as shown in FIG. 2A so that the wafer 3 may be placed within the diffusion box 1, which includes the diffusion source as shown in FIG. 2B. Therefore, the impurities of the diffusion source activated due to the heaters 5 are diffused into the wafer.
After a predetermined time, the slider 4 is pulled to the arrow as shown in FIG. 2C and thereby the wafer 3 is removed from the diffusion box 1. Therefore, the diffusion process is terminated.
However, as this conventional impurity diffusion apparatus cannot diffuse into more than one wafer at a time, the conventional apparatus and process are employed for a research development. Also, as the apparatus can not diffuse a plurality of wafers in a same environment, mass production is difficult and stability of diffusion characteristics for each wafer cannot be obtained due to insufficient diffusion depth, and diffusion concentration.